不使用列表索引:

listit = [1, 5, 3, 7]

x_position = 0
result = 0

for x in listit:
    x_position += 1
    y_position = 0
    for y in listit:
        y_position += 1
        if x_position < y_position:
            print(f"{x} * {y}")
            result += x * y
            print(result)

print(result)